1. Field of the Invention
The present invention relates to an image projection apparatus, particularly to an image projection apparatus whose projection optical system is interchangeable.
2. Description of the Related Art
Image projection apparatuses project light modulated by a light modulating element (also called as an image-forming element) such as a liquid crystal panel through a projection optical system onto a projection surface such as a screen to display a projection image. In order to display the projection image in a user's desiring region, it is necessary to adjust projection conditions such as an orientation (direction) and an oblique angle (inclination) of the image projection apparatus. However, changing the projection conditions causes in the projection image geometric distortion such as trapezoidal (keystone) distortion.
Japanese Patent Laid-Open No. 04-42679 discloses an image projection apparatus that detects an installation angle of the apparatus and performs geometric distortion correction on the basis of the detected installation angle to display on a screen a projection image including no distortion. Japanese Patent Laid-Open No. 2005-301317 discloses an image projection apparatus that performs image processing (sharpness adjustment) in response to change of an optical characteristic of its projection optical system with interchange thereof.
However, the image projection apparatus disclosed in Japanese Patent Laid-Open No. 04-42679 does not consider that an optical characteristic of its projection optical system is changed with interchange thereof. Therefore, inadequate geometric distortion correction may be made for the interchanged projection optical system, which may make it impossible to display a projection image including no distortion.
Moreover, the image projection apparatus disclosed in Japanese Patent Laid-Open No. 2005-301317 only performs the sharpness adjustment in response to the change of the optical characteristic with the interchange of the projection optical system, but does not perform geometric distortion correction.